arXiv subjects

R. E. Taam

Publications and source records attributed to R. E. Taam.

22 records · Page 2Linked to original sources

arXiv2001

Disks surrounding Cataclysmic Binaries

Observations of Cataclysmic Variables show a number of phenomena that do not fit easily into the standard magnetic braking scenario. These include the large spread in mass transfer rates, the low surface temperatures of many of the companion stars, and evidence for material at low velocities. We propose that these anomalies have a common cause: the presence of a circumbinary (CB) disk. This may be a significant component of mass transferring binaries in general. Direct detection of such CB disks may be possible but difficult, because of their low luminosity Disks surrounding Cataclysmic Binaries and spectral energy distribution peaking in the mid-IR.

astro-ph↗

arXiv2001

A Compton Up-scattering Model for Soft Lags in the Lower Kilohertz QPO in 4U1608-52

An empirical Compton up-scattering model is described which reproduces both the fractional amplitude (RMS) vs. energy and the soft time lags in the 830 Hz QPO observed in 4U1608-52 on Mar. 3, 1996. A combination of two coherent variations in the coronal and soft photon temperatures (with their relative contributions determined by enforcing energy conservation) gives rise to the QPO's energy dependent characteristics. All input parameters to the model, save a characteristic plasma size and the fraction of Comptonized photons impinging on the soft photon source, are derived from the time-averaged photon energy spectrum of the same observation. Fits to the fractional RMS and phase lag data for this kilohertz QPO imply that the spatial extent of the plasma is in the range from 4 to 15 km.

astro-ph↗

arXiv1996

Hydrodynamical Studies of Wind Accretion Onto Compact Objects: Two-Dimensional Calculations

We present the results of hydrodynamical simulations of nonaxisymmetric gas flow past a gravitating compact object in two dimensions. Calculations were performed with uniform flow as well as with transverse velocity and density gradients. We find that the flow is highly nonsteady, exhibiting the ``flip-flop'' behavior seen in previous studies in which accretion disks form with alternating directions of rotation. We investigate the periodicity of the flip-flop behavior, and study the effects of spatial resolution on the results. We find that the flip-flop motion creates accretion torques which, in some cases, may be large enough to explain the erratic spin behavior observed in some massive X-ray pulsars.

astro-ph↗

arXiv1996

GRO J1744-28: Last Gasps of a Dying Low-mass X-ray Binary

We argue that the bursting, transient X-ray source GRO J1744-28 is a binary consisting of a very low-mass ($M \approx 0.2 M_\sun$), highly evolved giant star that is transferring mass by Roche lobe overflow onto a high-mass ($M \approx 1.8 M_\sun$) neutron star. We explore a picture in which the bursts are due to thermonuclear flashes in matter that has accreted onto the neutron star. We attribute the unusually hard spectra of the bursts and the high burst rate compared to normal Type I X-ray burst sources -- indeed the existence of unstable nuclear burning itself -- to the unusually strong surface magnetic field, $ B_s \approx 1 \times 10^{13}$ G, of the neutron star.

astro-ph↗